The straight red lines come from the performance model presented and
are plotted for matrix times vector speeds of 50, 100, 200 and 400 MF.
We need to run at a large enough value of L so that the measured bandwidth
is above the red line (for what ever speed our processor achieves for
the corresponding value of L).

Pushing up the communication rate for small messages is important.

It is especially nice when we don't need more expensive hardware. There is
a huge price range among Quadrics, Myrinet and Fast Ethernet.